1. Field of the Invention
The present invention relates to a method of introducing at least one gene encoding a member of the transforming growth factor .beta. superfamily into at least one mammalian connective tissue for use in regenerating connective tissue in the mammalian host. The present invention also relates to a connective tissue cell line that harbors a DNA vector molecule containing a gene encoding a member of the transforming growth factor .beta. superfamily.
2. Brief Description of the Related Art
In the orthopedic field, degenerative arthritis or osteoarthritis is the most frequently encountered disease associated with cartilage damage. Almost every joint in the body, such as the knee, the hip, the shoulder, and even the wrist, is affected. The pathogenesis of this disease is the degeneration of hyaline articular cartilage (Mankin et al., J Bone Joint Surg, 52A: 460-466, 1982). The hyaline cartilage of the joint becomes deformed, fibrillated, and eventually excavated. If the degenerated cartilage could somehow be regenerated, most patients would be able to enjoy their lives without debilitating pain. There has been no method reported to date to regenerate damaged hyaline cartilage.
Traditional routes of drug delivery, such as oral, intravenous or intramuscular administration, to carry the drug to the joint are inefficient. The half-life of drugs injected intra-articularly is generally short. Another disadvantage of intra-articular injection of drugs is that frequent repeated injections are necessary to obtain acceptable drug levels at the joint spaces for treating a chronic condition such as arthritis. Because therapeutic agents heretofore could not be selectively targeted to joints, it was necessary to expose the mammalian host to systemically high concentrations of drugs in order to achieve a sustained, intra-articular therapeutic dose. Exposure of non-target organs in this manner exacerbated the tendency of anti-arthritis drugs to produce serious side effects, such as gastrointestinal upset and changes in the hematological, cardiovascular, hepatic and renal systems of the mammalian host.
In the orthopedic field, some cytokines have been considered as candidates for the treatment of orthopedic diseases. Bone morphogenic protein has been considered to be an effective stimulator of bone formation (Ozkaynak et al., EMBO J, 9:2085-2093, 1990; Sampath and Rueger, Complications in Ortho, 101-107, 1994), and TGF-.beta. has been reported as a stimulator of osteogenesis and chondrogenesis (Joyce et al., J Cell Biology, 110:2195-2207, 1990).
Transforming growth factor-.beta.(TGF-.beta.) is considered to be a multifunctional cytokine (Sporn and Roberts, Nature (London), 332:217-219, 1988), and plays a regulatory role in cellular growth, differentiation and extracellular matrix protein synthesis (Madri et al., J Cell Biology, 106:1375-1384, 1988). TGF-.beta. inhibits the growth of epithelial cells and osteoclast-like cells in vitro (Chenu et al., Proc Natl Acad Sci, 85:5683-5687, 1988), but it stimulates enchondral ossification and eventually bone formation in vivo (Critchlow et al., Bone, 521-527, 1995; Lind et al., A Orthop Scand, 64(5): 553-556, 1993; and Matsumoto et al., In vivo, 8:215-220, 1994). TGF-.beta.-induced bone formation is mediated by its stimulation of the subperiosteal pluripotential cells, which eventually differentiate into cartilage-forming cells (Joyce et al., J Cell Biology, 110:2195-2207, 1990; and Miettinen et al., J Cell Biology, 127-6:2021-2036, 1994).
The biological effect of TGF-.beta. in orthopedics has been reported (Andrew et al., Calcif Tissue In. 52:74-78, 1993; Borque et al., Int J Dev Biol., 37:573-579, 1993; Carrington et al., J Cell Biology, 107:1969-1975, 1988; Lind et al., A Orthop Scand. 64(5):553-556, 1993; Matsumoto et al., In vivo, 8:215-220, 1994). In mouse embryos, staining shows that TGF-.beta. is closely associated with tissues derived from the mesenchyme, such as connective tissue, cartilage and bone. In addition to embryologic findings, TGF-.beta. is present at the site of bone formation and cartilage formation. It can also enhance fracture healing in rabbit tibiae. Recently, the therapeutic value of TGF-.beta. has been reported (Critchlow et al., Bone, 521-527, 1995; and Lind et al., A Orthop Scand, 64(5): 553-556, 1993), but its short- term effects and high cost have limited wide clinical application.
Intraarticular injection of TGF-.beta. for the treatment of arthritis is not desirable, because the injected TGF-.beta. has a short duration of action, as TGF-.beta. is degraded into inactive form in vivo. Therefore, a new method for long-term release of TGF-.beta. is necessary for the regeneration of hyaline cartilage.
There have been reports of regeneration of articular cartilage with autotransplantation of cartilage cells (Brittberg et al., New Engl J Med 331:889-895, 1994), but this procedure entails two operations with wide excision of soft tissues. If intraarticular injection is enough for the treatment of degenerative arthritis, it will be of great economic and physical benefit to the patients.
Gene therapy, which is a method of transferring a specific protein to a specific site, may be the answer to this problem (Wolff and Lederberg, Gene Therapeutics ed. Jon A. Wolff, 3-25, 1994; and Jenks, J Natl Cancer Inst, 89(16): 1182-1184, 1997).
U.S. Pat. Nos. 5,858,355 and 5,766,585 disclose making a viral or plasmid construct of the IRAP (interleukin-1 receptor antagonist protein) gene; transfecting synovial cells (U.S. Pat. No. 5,858,355) and bone marrow cells (U.S. Pat. No. 5,766,585) with the construct; and injecting the transfected cells into a rabbit joint, but there is no disclosure of using a gene belonging to the TGF-.beta. superfamily to regenerate connective tissue.
U.S. Pat. Nos. 5,846,931 and 5,700,774 disclose injecting a composition that includes a bone morphogenesis protein (BMP), which belongs to the TGF .beta. "superfamily", together with a truncated parathyroid hormone related peptide to effect the maintenance of cartilaginous tissue formation, and induction of cartilaginous tissue. However, there is no disclosure of a gene therapy method using the BMP gene.
In spite of these prior art disclosures, there remains a very real and substantial need for a method of introducing at least one gene encoding a product into at least one cell of a connective tissue of a mammalian host in vitro, or alternatively in vivo, for use in treating the mammalian host. Further, there is a need for a process wherein a gene encoding a member of the transforming growth factor .beta. superfamily is used to regenerate connective tissue in the mammalian host. More specifically, there is a need for a process where a gene coding for a TGF-.beta. superfamily of proteins is expressed in host connective tissue cells in vivo.